The forward has a nagging groin problem but was forced to start their opening 2-0 defeat by the Netherlands on Monday when Jon Dahl Tomasson pulled out with injury.
He made little impact in his hour-long stint before being substituted but Olsen believes Bendtner, very inconsistent for club side Arsenal, can still be influential.
"Perhaps he can play 90 minutes for us tomorrow, I don't know, but it's true he is an important player," a grumpy-looking Olsen told a news conference on Friday.
"Nicklas and all of our medical team have done a wonderful piece of work, it's a miracle actually that he is able to play.
"But we have to be cautious what we can go do with him in training, he has only been training every other day."
Former Denmark defender Martin Laursen, whose career was wrecked by injury, was dubious about Bendtner's participation.
"He is not fit. He says he is ready but he is not at his best. It's a shame," he told Reuters.
All the team trained on Friday including Bendtner and Tomasson but Olson was coy about whether the latter was fit to play in Pretoria on Saturday.
Despite losing the opener, Olsen would take a draw against Cameroon especially if the result between the Netherlands and Japan earlier in the day helps his team.
"Yes we'll know the result. I'm happy we are playing after the other match in the group. We don't know how it will influence us," he said.
"Perhaps we'll end up being happy with a point but sure we have to get something from the game."
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